華嚴經探玄記 14.14

14.14

第四淨佛國土分中有三自在：一器世間自在行、二眾生世間自在行、三智正覺世間自在行。初是化處、次是所化、後是能化。具後二淨，方名淨土。於此三法起化無礙，故名自在。

In the fourth [section], on the division of purifying the Buddha lands, there are three masteries: first, the practice of mastery regarding the receptacle world; second, the practice of mastery regarding the sentient-being world; third, the practice of mastery regarding the enlightened-wisdom world. The first is the place of transformation; the next is that which is transformed; the last is that which transforms. Only when endowed with the purity of the latter two is it called a "pure land". Generating transformations without obstruction with respect to these three dharmas is therefore called "mastery".